Biocarvão da casca de coco verde enriquecido com ureia como forma de mitigar a lixiviação de nitrogênio em solos.

Abstract

Coconut farming is a major generator of waste, mainly green coconut husk, resulting from the production of coconut water in agro-industries. These residues can be converted into biochar (BC), a carbonaceous product, from the biomass thermodegradation. When added to urea, BC can constitute a sustainable alternative for the use of these residues and as a potential nitrogen (N) losses mitigator through the leaching process, when applied to the soil, thus improving edaphic quality. In this context, the objectives were: to characterize BCs from green coconut husk residues produced at 400, 500, 600 and 700 °C, to evaluate the adsorption capacity of ammonium (N-NH4 + ) and nitrate (N-NO3 - ) in solution, of the BCs produced at temperatures of 400 and 700 °C; and to evaluate the leaching of N-NO3 - and N-NH4 + in soils of different textures after the addition of urea-enriched biochars, as well as to relate this influence with the leaching of other nutrients (Ca, Mg and K) in the soil. Increasing the temperature to 700 °C produced BCs that were more alkaline (pH=10.8) and with a pHPCZ twice as high compared to that produced at 400 °C. At higher temperatures, BCs showed higher K and Ca concentrations. BCs produced at lower temperatures have higher yields, volatile material content and fixed carbon. CEC and AEC were increased by 2 and 4 times in BCs produced at a temperature of 700 °C, which exhibited maximum capacity to adsorb N-NH4 + and N-NO3 - higher than 17 and 70%, respectively, when compared to BCs produced at 400°C.The BC produced at 700 °C, due to its higher N adsorption capacity and better physicochemical characteristics, was used in the leaching test. Two urea doses, 200 mg kg-1 (100%) and 100 mg kg-1 of soil (50%) were used as experimental control units, to be added to BC. The treatments were as follows: 50% (T1) and 100% (T8) of the urea dose, 50% urea + 10% BC (T2), 50% urea + 20% BC (T3), 50% urea + 30% BC (T4), 100% urea + 10% BC (T5), 100% urea + 20% BC (T6), 100% urea + 30% BC (T7). After the application of the treatments in the soils, the leaching events were carried out after 3, 7, 14, 21 and 28 days, and the leached material was collected for further analysis of the concentration of N-NH4 + and N-NO3 - . The results demonstrate that the use of BC enriched with urea (T2 and T6 treatments) reduced by up to 6 and 93%, respectively, the leaching of N-NH4 + during the 28 days of evaluation, compared to their respective control treatments in very clayey soil, and 32% (T4) and 48% (T6) in predominantly sandy textured soil. Reduction for N-NO3 - leaching, in treatments T4 and T6, was also observed. Different correlations were observed between nutrient leaching in the studied soils. The product of the addition of biochar from the green coconut husk produced at 700 ºC in the composition of mineral fertilizers, particularly urea, is a material with high potential for mitigating the losses of inorganic N in soils, Ca, Mg and K, regardless of texture.